SE 6550 Guitar amp - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th April 2013, 09:17 PM   #1
wobuse is offline wobuse  United States
diyAudio Member
 
wobuse's Avatar
 
Join Date: May 2011
Default SE 6550 Guitar amp

Hi all.
Here is a a Single Ended guitar amp that i put together for a friend.
He is looking for a cleaner ,country kinda sound, so i put together this schematic from a variety of others,on the net. it is up & works great..but I may tweak a few things.Anyone care to look at the component values & add their opinions ,I would be grateful. I am thinking about increasing some of the series resistance to tame the gain a bit.
Thanks In advance.

RG6550.pdf
Here is a picture of the chassis ..I still have to build a case for it.
Click the image to open in full size.

Last edited by wobuse; 5th April 2013 at 11:57 PM.
  Reply With Quote
Old 5th April 2013, 10:47 PM   #2
diyAudio Member
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
Some quick comments (I assume most of these are drawing errors, and not in the actual cicuit):

- remove all the grid to cathode connections (to the bypass caps);
- the EF86 is missing the screen bypass capacitor, typical value is 10n-100nF;
- all the coupling capacitors' (C3, C9, C10, C11) value seem high;
- Volume 2 is mis-wired, the grid should be connected to pin 2 of RV3;
- R13, R14 & R16 are probably typo's - 200K instead of 2K?
- R23, the 470R seem quite high for the 6550, what output transformer are you using?

Cool looking chassis you got, did you make it yourself?

Jaz
  Reply With Quote
Old 5th April 2013, 11:53 PM   #3
wobuse is offline wobuse  United States
diyAudio Member
 
wobuse's Avatar
 
Join Date: May 2011
Quote:
Originally Posted by jazbo8 View Post
Some quick comments (I assume most of these are drawing errors, and not in the actual cicuit):

- remove all the grid to cathode connections (to the bypass caps);
- the EF86 is missing the screen bypass capacitor, typical value is 10n-100nF;
- all the coupling capacitors' (C3, C9, C10, C11) value seem high;
- Volume 2 is mis-wired, the grid should be connected to pin 2 of RV3;
- R13, R14 & R16 are probably typo's - 200K instead of 2K?
- R23, the 470R seem quite high for the 6550, what output transformer are you using?

Cool looking chassis you got, did you make it yourself?

Jaz
Thanks for looking at the schematic .i didn't realize there where so many errors.
Most of what you listed where schematic errors except.....
I don't have a screen bypass cap for the EF86. Will look into that .
The bypass caps could be high but I don't seem to notice a problem.
I don't think R13 , R14 & R16 are typos ,,,I prolly should raise them.
R23 is high,but I am purposely bias the 6550 pretty cold . The power tranny seems happeir that way.I salvage the chassis ,and trannys of an old Stromberg Carlson tube amp. (SE 10watt 6L6). I am just using the 6550 for its 'stiffer' sound.I did make the front panels from scratch.I will post sum pics of that process soon, but 1st; I have a schematic to edit.
  Reply With Quote
Old 6th April 2013, 02:33 AM   #4
wobuse is offline wobuse  United States
diyAudio Member
 
wobuse's Avatar
 
Join Date: May 2011
Ok..
Here is the updated schematic....RB6550.pdf

I fixed the errors ,also I updated it to reflect changes I made in the actual amp.


Here some pictures of the face plate build....

Take one sheet of aluminum,,,add lots of elbow grease...
Click the image to open in full size.

Bend a piece of perforated metal ...

Click the image to open in full size.

Paint them pretty colors....Click the image to open in full size.



Then rivet the whole mess together....
Click the image to open in full size.


I used a laser printer to make clear water transfers ,to label the front panel....

Click the image to open in full size.
  Reply With Quote
Old 6th April 2013, 04:00 AM   #5
wobuse is offline wobuse  United States
diyAudio Member
 
wobuse's Avatar
 
Join Date: May 2011
So .. What are some of the implications of make the coupling caps too large. Tubey bass? Blocking distrotions?
  Reply With Quote
Old 6th April 2013, 05:37 AM   #6
diyAudio Member
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
I really like what you did with the front panel - it really stands out - not like your typical tolex-on-a-piece-of-wood construction... Yes if the coupling capacitors are too large, the they are likely to cause blocking distortion - but if you don't hear it now, then you can just leave them alone.

Jaz
  Reply With Quote
Old 6th April 2013, 05:40 AM   #7
diyAudio Member
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
I really like what you did with the front panel - it really stands out - not like your typical tolex-on-a-piece-of-wood construction... Yes if the coupling capacitors are too large, then they are likely to cause blocking distortion - but if you don't hear it now, then you can probably just leave them alone.

Jaz
  Reply With Quote
Old 9th April 2013, 11:31 PM   #8
diyAudio Member
 
Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
disclaimer: I'm just a hack...YMMV

c 3,9,10, 11 are not bypass caps, they're interstage coupling caps. Large values just carry a bit more bass, at risk of some grid-blocking if you're overdriving (and possibly wasting some of the limited power on string movements below the frequencies of interest). For your country-clean objective it might be OK, but if (when dirty) the volume ducks and recovers with a slow swell, reducing the bass thry the coupling caps may help. If he doesn't use boost pedals, you might be fine if if sounds good to you, especailly for D-tuned texas guitar or baritone guitar.

Assuming your power supply was up to it, you could switch the two channels one stage earlier than where you mix them now. That would save a stage and switching instead of mixing would add some gain, and you wouldn't need a dual pot. Then you could use that 'extra' stage (which you saved from duplicating in both channels) direct-coupled for more current to drive a pair of 6550's and a speaker load with a lower impedance. That would get you louder before breakup, another way of saying "more clean". A relay (or two) and you've got remote channel-switching. But that would be a different amp, and I assume you know what you want.

You want cleaner; is it the preamp or power amp that breaks up first? If you really need more watts, tweeking the preamp won't help.

Usable clean is the dynamic range from noise floor to breakup, so you might work on the noise too. Again, I like swtiching channels instead of mixing, but mixing worked for Fender it can work for you. An efficient low-power speaker with a small voice coil in an open-back cabinet will get twice as loud before breakup. Then you start working on getting rid of all hum. It never ends. Best of luck, have fun.

Now that's a weird tone select to my experience...no slope control
  Reply With Quote
Old 10th April 2013, 12:49 AM   #9
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Large coupling caps pass more bass. Depending on the guitar, pickups, and strings, you may be getting more bass than you need. Bass uses up the most of your amps power, hits the OPT harder and takes up the most of your speaker's capability. Reducing the coupling cap size can often allow the amp to play louder, especially if you have a smallish OPT or speaker.

There are places where I use a .1uF or larger coupling cap, especially if the amp has a lot of power, a big OPT and might see a bass guitar or a keyboard. For a guitar only amp, I start with .022 and tweak as needed.

I built several "Turbo Champs" about 15 years ago that used a single 6550 on 430 volts through a Hammond 125CSE. Every one of these was different, just made up as I went along. Many were for my daughters friends. Each one was tweaked with the users guitar and speaker choice. If the user liked two choices, he got them, on a switch. They all got a switch on the OPT to intentionally mismatch the speaker. Most got a tube / solid state rectifier switch, and a switch to add more capacitance to the power supply. Contrary to some opinion, a class A amp isn't class A as soon as you drive it into distortion, so power supply sag does have an effect. The cathode bypass caps were switchable on some amps.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 10th April 2013, 02:09 AM   #10
wobuse is offline wobuse  United States
diyAudio Member
 
wobuse's Avatar
 
Join Date: May 2011
Thanks for the great advice guys. Much appreciated !
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
SE 6550 mr2racer Tubes / Valves 3 16th October 2012 11:20 AM
New to tubes, SE guitar amp Debo Instruments and Amps 6 16th July 2012 09:51 PM
6550 se amp Chad Tubes / Valves 3 15th September 2011 05:48 PM
SE P-P guitar amp. Printer2 Tubes / Valves 10 7th April 2011 01:51 AM
Se 6550 dr.socrates Tubes / Valves 11 12th February 2010 06:24 PM


New To Site? Need Help?

All times are GMT. The time now is 02:34 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2